Method of producing high tensile strength iron



metalloids can be held Within very close prede.

Patented Aug. 15, 1939 PATENT OFFICE METHOD OF PRODUCING man TENSILE STRENGTH IRON James L. Gibney, Buifalo, N. Y.

No Drawing. Application September 18, 1936, Serial No. 101,416

6 Claims.

This invention relates to a method of making high tensile strength hyper-eutectoid iron andmore particularly to iron suitable for casting and having a carbon content of from .90-2.00% and in which the amount of carbon and other termined or definitive limits and, in particular, in which the iron has a low phosphorus content to assure good castings;

In general the present invention comprises carbon and low metalloid content, preferably by treating the same in an electric furnace for an insufiicient length of time to provide an iron that is commercially usable; mixing the molten A and B irons without further heating or other processing in a ladle or other suitable vessel to produce the C iron or an end product having the desired constituents and casting the C iron so as to produce a resultant hypereutectoid material. By withdrawing the B iron from the electric furnace before it is finished, preferably at the end of the melt-down, only a partial reduction of the metalloids takes place; the final composition of the iron can be accurately controlled by controlling the composition of the charge; and the total heat added in the electric furnace is reduced to a minimum thereby providing a rapid solidifying material without pronounced dendritic patterns. The B metal is withdrawn in a partially refined condition, the small amount of. gas or oxides, if any, present because of the partially refined condition of the B iron being absorbed by the silicon, manganese and carbon in the A iron. The composition of the A and B irons can be easily controlled and also easily determined by simple fracture tests thereby permitting of accurately controlling the composition of the C iron. The composition of irons in the .902.00% carbon range cannot be accurately determined by fracture tests but would require a laboratory analysis. Hence in prior methods of making irons in this range in a single furnace or .a final single furnace, fracture tests could not be used with any degree of accuracy.

It will therefor be seenthat the principal object of this invention is to provide a simple process of commercially producing .90-2.00% carbon hyper-eutectoid iron. Other objects are to provide a process for producing such iron in which:

(A) The proportions of all of the elements in the finished metal can be veryaccurately pre-v determined without the usual continuous samplings, laboratory tests and adding of various ingredients to the molten bath or baths from time to time (B) The phosphorus content of the finished product is low, thereby avoiding the formation of Steadite, -high phosporus eutectic and massive r dendrites, thus producing a rapid setting iron;

(C) The B or electric furnace iron is only partly finished and no manganese or silicon is added, thereby providing a low temperature C iron which rapidly solidifies in the molds without massive dendritic formations or primary crystallities;

(D) The process can be carried on with the usual foundry equipment in iron and steel works,. thereby permitting the ordinary foundry to produce hyper-eutectoid iron in competition with steel and so-called semi-steels of comparative characteristics. As the A iron, a part of the usual run of cupola iron used in the everyday production of castings in the foundry is employed; I

(E) The small amount of gases or oxides, if any, present in the B iron, caused by the unfinished or unrefined state of this iron, are absorbed by the metalloids in the A iron so that the castings are free from porosity and are uniform in structure; 1

(F) The iron can be alloyed at any stage with a other metals, such as chromium, nickel, molybdenum, copper, aluminum, etc.';

(G) Very little time is required to produce the C iron in condition for pouring, the A iron being available as a part of the regular foundry casting iron and the B iron requiring less than 40 an hour to produce with suitable equipment;

(H) The cost of producing the C iron is therefore less than the cost of producing steels and so-called' semi-steels of comparative characteristics; 5

(I) The material or C iron sets quickly with less shrinkage, thereby providing a high yield, by weight, in castings per pound of iron melted and also avoid internal defects, such as pipes, shrinks and voids, as well as pronounced dendritic patterns, the absence of such defects increasing the yield of sound, saleable castings;

(J) Alloys are not necessary to compensate for the discrepancies of graphitic dispersions occurring in the customary methods of production of common irons;

'(K) To provide a process in which the amount of silicon in the finished product can be extremely accurately controlled within predetermined limits as compared with any other melting method utilizing an acid process or carried on with high temperatures in the presence of high carbons. 4

The invention is directed to the production of high' tensile strength, low phosphorus, hypereutectoid irons suitable for casting into ingots and/or finished castings having a carbon content of from .902.00%. In such hyper-eutectold irons the carbon as precipitated in the casting is found as iron carbide (FeCa) it precipitating at the boundaries of the pearlitic grains andthroughout the grain proper. This produces a hard brittle iron casting which responds readily to heat treatment. The final form of carbon in the heat treated casting is in the form of a small nodular graphite or a spheroidized cementite and is quite unlike the weak, large flake graphitic dispersions present in common grey irons and socalled high test irons. The use ofsuch nvpereutectoid iron has distinct advantages where high tensile strength is desired because of its high' strength accompanied by high elasticity limit, impact, torsional-resistance and high moduli of elasticity, but because of ,the difficulty heretofore experienced in producing such hyper-eutectoid irons commercially and of uniform quality, it has been the practice where, say, strength above 60,- 000 lbs. per square inch were desired, to alloy 200-3.25% carbon iron with alloys such as molybdenum, chromium, copper, etc. However, but

few of such alloying metals produce the marked toughness of the hyper-eutectoid iron forming the subject of this invention andthere are 'but few of such irons with alloys that can resist the impact of a'd'ynamic shock.

As illustrating the importance 'of' the commercial production of hyper-eutectoid iron, especially common or unalloyed iron in the .902.00% carbon range, the development of cast alloy crank shafts and cam shafts by a large manufacturer (Ford Motor Company and aifili'ates) is in point. If it had been commercially possible to produce a common iron having the remarkable properties of the iron to which the present invention relates, such ironwould probably be generally adopted for such uses. However, due

tothe discrepancies of high graphitic dispersion. and consequent weakness and low amount of ductility of such irons as heretofore produced, such common irons-have not been employed and instead the Ford crank shafts are made with 1.25-1.60% carbon and .carry copper and chromium as toughness producing elements after suitable heat treating. After such heat treatment these finished alloyironcrankshaftspossess remarkable properties of toughness, resiliency, torsional resistance and hardness far superior to regular irons made by cupola methods, this 'being' due to the factthat the iron used is within the So-2.00% carbon range with the deficiencies heretofore existing in the cupolaor air furnace production of such hyper-eutectoid iron in part compensated for by the addition of alloys and multi-sta ge processing. 'As previously stated, myinvention comprises preparing an A' iron, preferably in a cupola,

and having an easily controlled predetermined metalloid OOIitGIit determined, if desired,

by a fracture test; preparing 'a B iron, preferably in an electric furnace, by subjecting the charge of low phosphorus and sulfur content iron' to a melt-down only so far as to be partially finished and to enable ready control of the metalloid content and then mixing the A and B irons in a ladle or other suitable vessel in Production of the "Airon The molten A iron is 'best roduced by melting the materials in a cupola furnace for the production of irons coming within the 3.00- 3.50% carbon range. However, in producing C iron in the lower carbon range, for example, a .90% carbon iron, an air furnace or any other form of furnace may be used to produce A iron having less than 3.00% carbon, as is well understood in the art. In most foundries A" iron, within the specifications required for the present process, would be used generally in making common grey iron and high test iron castings. It is therefore assumed that such castings would absorb a part of the cupola production and that, say, 50% or 10,000 pounds of A" iron will be held in the ladle or forehearth, a 48-inch cupola having a 20,000 pound capacity being assumed. The time when the cupola is started will depend entirely on the time of .day the molds for' the days' work in pouring the grey or high test iron will be ready, because the electric furnace can melt the B iron at any hour running close to the scheduled time when hot C iron may be required. The duration of the heat in the electric furnace is only an hour or so or less than an hour with modern equipment becausethe B" iron in the electric furnace is only partially finished and requires less than half the time of regular production of electric steel for casting purposes. In accordance with usual practice, the cupola is made ready early in the morning and after the coke bed is properly made up and heated to good ignition, the melter builds up the first charge or 2500 pounds of pig iron and returns somewhat free from sand and rust. A charge of 200 pounds of coke is then placed'evenly over the metal charge and subsequent alternate charges of 2000 pounds of intermixed pig iron and scrap and 200 pounds of coke are built up in the cupola until the final iron charge has been placed in the cupola. The air blast is then put on and in about ten mnutes the tap hole is opened and the iron As only half of the iron produced is flows out. assumed to be used in the present example, the general foundry can use the excess iron flowing from the cupola since it is within the workable specfications, additions of aluminum, ferro-silicon or alloys, if necessary, being made in the ladle to The control of the carbon is preferably such that the regular product coming from the cupola will average between 3.00 and 3.50% carbon, this I control being important in the production of a consistently uniform 0" iron. This is distinctly not saturated or supersaturated carbon iron but is theusual high grade grey or high test iron produced by a cupola or other furnace. The

v possible ranges of the metalloids in the 11" iron may be as follows:

Percent Carbon 3.00-3.50 Manganese .30-5.00 Silicon .306.00 Phosphorus .02" .50 Sulfur .02 .50

However, in the practical manufacture of hyper-eutectoid iron in accordance with my invention I prefer to confine the metalloid content of the A iron to the following:

Percent Carbon 3.00-3.50 Manganese .80-1.20 Silicon 2.00-2.70 Phosphorus, maximum .10 Sulfur, maximum .10

Production of the B iron For best control of the analysis of the B iron I favor an acid electric furnace. It is assumed that equal weights of A and B" irons will be mixed to compose the C iron and therefore the charge melted in the electric furnace will be 10,000 pounds of metal. Since an important feature of my invention is the production of a low phosphorus and low sulfur final product, it is preferable to charge the electric furnace with iron having a phosphorus and sulfur content as low as commercially practicable without getting into premium grades of high priced low phosphorus steel scrap. Regular No. 1 grade of electric furnace melting steel is satisfactory, this being commonly known as acid electric furnace melting scrap, the phosphorus usually being under .04% and fairly uniform. In this scrap the carbon is under .40% and the sulfur under 04%. Other low phosphorus grades can be used advantageously.

During the operation of the electric furnace, the melter may add a shovel of ore, mill scale and possible limestone to melt the heat down to a low carbon content. The charge in the electric furnace is not finished or carried through to the point where commercial steel is produced. In-

- stead the iron is preferably withdrawn immedifrom a solid to a molten state. During the melt down, the carbon, manganese and silicon are reduced. Since an acid electric furnace is employed there is no reduction of the phosphorus and sulfur during the melt-down, the scrap used as the charge having purposely been selected for its low phosphorus and sulfur content to insure a low phosphorus and low sulfur C iron.

The 'B iron is distinctly not pure or completely decarburized iron but is unfinished steel not capable of being used for casting and may contain some gaseous products. The metal is purposely Withdrawn in an unfinished state to reduce the time required to produce the 0" iron; reducethe heat added to the charge in the electric furnace and thereby produce rapid setting C iron and the gaseous products, if. any, do not interfere with the process as the gases are immediately absorbed by the silicon, manganese and carbon in the"'A iron when the A silicon-zirconium could be added to the molten B iron to quickly absorb these gases, but I have found that it is not ordinarily necessary. It is undesirable to add silicon or manganese to the molten B iron as their reaction with the charge is heat producing and hence tends to raise the heat of the (13" iron melt and reduce the rapid setting qualities of the C iron. The addition of silicon and manganese to, the molten 13 iron is unnecessary as with the proper selection of the charge, the composition of the bath at the end of the melt-down can be accurately forecast. Hence B iron of exact and consistently uniform' analysis can be readily produced. Further, the character of the B iron can be readily determined by a simple fracture test, a laboratory analysis being unnecessary.

The production of the B iron does not require any slag making procedures and also because it is interrupted at the end of the meltdown is unlike any process used in the making of low carbon-steel for the production of special castings or ingots. The iron tapped from the electric furnace will have a temperature of between 1580-1650 C. It is desirable tostay on the minimum side of this temperature range since under cooling may otherwise be required.

It will be understood that if desired, metal alloys such as copper, nickel, chromium, molybdenum, tungsten, etc. may be added in the electrio furnace.

The possible ranges of the metalloids in the However, I prefer that at the end of the meltdown the B iron, ready for mixing with the A iron, have the following analysis:

Per cent Carbon ,.03-.50 Manganese .03-.50 Silicon O3-.50 Phosphorus, maximum Sulfur, maximum Production of the C. Iron The A iron has been held in the forehearth, ladle or other suitable vessel ready for mixture ,i'llith the B iron, the excess of A" iron produced being used in the regular casting operation of the foundry.

In the example assumed, to the 10,000 pounds of. A iron in the ladle at a temperature of from l490 to 1566 C. is added the 10,000 pounds of "B'iron at a temperature of from 1580-1650 C.

The A and B irons immediately combined,

any gaseous products present in the 3" iron being absorbed by the silicon, manganese and' pronounced dendritic pattern would be formed in the finished product. By avoiding such patterns, the casting or casting material responds readily to heat treatment. Further, because of the low phosphorus content Steadite is not formed.

-' The C" iron is extremely rapid setting, thereby not'only avoiding the formation of the large primary crystallites but also. assuring small shrinkage and hence a greater commercial yield by weight in castings per pound of iron melted. The reduced shrinkage, in addition to providing a greater yield, also tends to provide a more solid casting material substantially free from internal defects. The shrinkage of the C" metal in the mold is approximately from V; to of an inch to the foot as compared with a shrinkage of about A of an inch to the foot with cast steel.

The range of the usual metalloids in the iron or finished product made by mixing the aforesaid A and ,B" irons is as follows:

Per cent Carbon"; .902.00 Manganese .50-1.50 Silicon .50-2.25 Phosphorus -.05 .15 Sulfur- .05- .15

The castings and/or ingots from the C iron are hard, brittle and unmachinable in the cast state but may be worked, unannealed, with special alloys such as tungsten. carbide. Fins, gates and risers canbe broken off clean by nicking with a chipping hammer. To render the casting usable for the purpose intended, it should be annealed or heat treated to develop machinability. How

ever, the absence of .a pronounced dendritic pattern' permits of annealing or heat treating the castings ina very short;time.

The heat treated castings made from the simple or unalloyed C iron produced in accordance with my invention possesses high strength, accompanied by-high elastic limit, impact and high moduli of elasticity. With the average or" socalled high test irons the graphitic carbon, which is the main constituent controlling strength, is in the form of weak, thick plates which impair the strength and prevent any ductility or any flow of the metal under stress. Consequently with such high test irons it has-been customary to add alloys and also superheat the molten metal at extreme temperatures to break up the large graphitic plates. With the hyper-eutectoid iron of the present invention, carbon of this form is not found, the carbon instead being in very fine which in most cases averages at least 60% of the maximum or ultimate strength. .The average properties of the simple or unalloyed hyper-eutectoid iron made in accordance with my inven- .tion are as follows: Tensile strength, lbs per sq. inch mini- Brinell hardness 200-500 Moduli of elasticity, lbs. per sq. inch minimum 25,000,000 The above are minimum properties, greatly increased, of course, by the use of the usuaispecial alloying metals and methods of heat treating alloyed iron.

It will be observed use of low temperatures and only partially rethat the process provides extremely accurate control of the silicon content of the finished product. This is due to the fining the charge, in an oxidizing or neutral atmosphere, in the electric furnace, thus avoiding the reduction of metallic silicon (SiO:+2C=

Si+2CO) from the acid or high silica lining or slag, if any, in the furnace.

From the foregoing it is apparent that the present invention providesa process which p'ermits of casting, commercially, hyper-eutectoid high tensile strength iron or ingots of consistently uniform and exact composition; the metal can be prepared in a relatively short time since the process involves mixing a regular run of constantly available cupola iron with a B iron that can be prepared in less than one hour; the

process is extremely simple and susceptible to exact control as the cupola" metal can easily be prepared to exact specification and the 3" metal partially refinedin the electric furnace can also beprepared to exact specification, more particularly in that the meltingof the 3" metal is only carried to the end of the melt-down; the

composition of both'the "A and B metalcan be readily determined by simple fracture tests to check or prove the exact composition of the C metal; the process does not require additions of various metalloids in thecourse of-proeessing to produce the desired composition, but such additions are purposely eliminated; phosphorus content and pouring temperature of the finished 0" metal is low thereby insuring rapid setting of the castings, reduced shrinkage 'and high yield, by weight, of castings per pound of metal melted and a-material substantially free from internal and external defects, large .dendritic patterns and Steadite formations; the process can be carried "on with the usual foundry equipment; the

gases, if any, present in the B metalareabsorbed by the metalloids in the A metal; and the iron can be alloyed with other metals at any stage; -the process permits of exact control of the silicon in the final product.

By unfinished steel" as used in the'followinfl claims, is meant a noncommercial or unusable steel melt. Such an unfinished steel is one that has not been completely refined or finished in the furnace, such as one taken out after very little attempt has been made to produce slags, which is not heat finished in accordance with the regular practice of a steel maker in making specification steels that must be made to low silicon, medium manganese content and the required balance of the other elements to provide a commercially usable steel. Further, the unfinished steel which I prefer to use as the 3" iron is gassy and could not be made into commercial castings. If an attempt were made to cast this unfinished steel the castings would be nonmachineable and highly dendritic and too hard and brittle to be annealed by the usual foundry treatments.

It will be understood that while I have described specific apparatus, procedure, formulae and percentages, the invention is in no sense to be limited thereto, but is to be accorded .the full range of equivalent apparatua procedure, formulae and percentages comprehended by the following claims. In particular the process can be carried out using in the production of the A and B metals, respectively, various combinations of melting equipment, Euch as: two electric furnaces; a Bessemer furnace and a cupola; two open hearth or air furnaces; an open hearth furnace and an electric furnace; a Bessemer fur,- nace and an open hearth furnace; a Bessemer furnace and an electric furnace and any other form or combination of furnaces.

I claim as my invention:

1. The method of producing high tensile strength hypereutectoid iron castings having a carbon content of from .90 to 2.00% which consists in preparing a low temperature molten iron, by remelting, having a carbon content of more than 2.00% and having at least 30% silicon and .30% manganese, preparing a partially finished steel of higher temperature by subjectinfig a raw material charge to a melt-down period in a furnace to reduce the carbon content to less than .90%, and mixing the first molten iron with the partially finished steel in proper proportion to produce a hyper-eutectoid iron of the desired carbon content and pouring said mixed iron into molds. Y

2. The method of producing high tensile strength hyper-eutectoid iron castings having a carbon content of from .90 to 2.00% which consists in preparing a low temperature-molten iron, by remelting, having a carbon content of more steel by subjecting a raw material charge to a melt-down period in a furnace to reduce the carbon content to less than .90% and to raise the temperature of the melt to a maximum of 1650 0., immediately mixing the first molten iron with the partially finished steel in proper proportion to produce a hyper-eutectoid iron of the desired carbon content, permitting the mixed irons to tent of more than 2.00% and having at least .30%

silicon and 30% manganese, preparing a partially finished steel of higher temperature by subjecting a raw.material charge to a melt-down period in an electric furnace to reduce the carbon content to less than .90%, and mixing the first molten iron with the partially finished steel without further heating or processing and in proper proportion to produce a hyper-eutectoid iron of the desired carbon content.

4. The method of producing hightensile strength hyper-eutectoid iron castings which consists in preparing a molten iron havinga carbon content of more than 2.00% at a temperature not exceeding 1566 C. and having at least 30% silicon and 30% manganese, preparing a partially finished steel by subjecting a raw material charge to a melt-down period in a furnace to reduce the carbon content to less than .90% and to raise the temperature of the melt to a maximum of 1650- 0., immediately mixingthe first molten iron with the partially finished steel without further heating or processing and in proper proportion to produce a hyper-eutectoid iron of the desired carbon content, permitting the. mixed irons to cool to less than 1600 C. and the cooled metal in the molds.

Pouring 5. The method of producing high tensile strength hyper-eutectoid iron castings which consists in melting iron to provide a melt having a maximum temperature of- 1566 C. and to have the following analysis:

Per cent Carbon 3.00-3.50 Manganese .30-5.00 Silicon Q .30-6.00 Phosphorus, maximum .50 Sulfur, maximum .50

preparing a partially finished steel by subjecting an iron charge to a melt-down period in an electric furnace to provide a melt having a maximum temperature of 1650 C. and to have the following analysis:

- Per cent C'arbon .03- .50

Manganese .03-2.00'

Silicon .03-6.00 Phosphorus, maximum .20 Sulfur, maximum -.10

immediately mixing the first molten iron with the electric furnace melt without further heating and in proper proportion to produce a hypereutectoid iron of from 1535 to1608 C. and of the following analysis:

Per cent Carbon .90-2.00 Manganese .50-1.50 Si'icon .50-2.25 Pnosphorus .05- .15 Sulfur .05- .15

and pouring the metal into molds.

6. The method of producing high tensile strength, hyper-eutectoid iron castings which consists in remelting iron to provide a melt having a maximum temperature of 1566 C. and to have the following analysis:

Per cent Carbon 3.00-3.50 Manganesenn; -.30-1.50 Silicon. 1.50-2.50 Phosphorus, maximum .10 Sulfur, maximum .15

and preparing a partially finished steel by subjecting. an iron charge to amelt-down period in an electric furnace to provide a melt having a maximum temperature of 1650 C. and to have the following analysis:

Carbon .03- .50 Manganese .75-1.50 Silicon .50-1.00 Phosphorus, maximum .06 Sulfur, maximum .06

immediately mixing the first. molten iron with the electric furnace melt without further heating and in proper proportion to produce a hypereutectoid iron of from 1535 to 1608 C. and of and pouring the metal into molds. ,7

JAMES L. GIBNEY.

Per cent 

